BX Past its lifespan?


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Old 04-15-19, 09:59 AM
Z
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BX Past its lifespan?

I was reading a recent post about crumbling BX insulation and it reminded me of a conversation I had a few months ago with an electrician about knob and tube and BX wiring. Wanted to get the experts' opinions.

We're all in agreement that knob and tube wiring is well past its lifespan. Not that it's necessarily a hazard in every single case, but there are many reasons to replace it.

This electrician was saying how BX is actually worse than K&T. Back then, they took the same cloth-covered wire and put it into an armored casing. With K&T, at least it had air-space to cool it. Once it was put into the casing, it easily overheats, degrading the insulation over the years.

I hadn't heard of any specific reasons to replace BX, other than if you wanted to extend it as its grounding is sometimes questionable through the armor.

Any thoughts on the subject?
 
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Old 04-15-19, 10:32 AM
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I think it's a case-by-case basis. If the cable has been over-fused or feeds a flush light fixture is where I see conductors in the worst shape. If it's just sitting inside the wall cavity it really should be OK as long as it's left undisturbed.

The break point for me is whether it's a natural rubber insulation or a plastic, and that transition was in the 1940s to 1950s. BX has been manufactured with both so it depends on the year and brand. The natural rubber & cloth stuff literally rots to dust eventually and both heat and moisture accelerates it. Plastic insulations theoretically should last several hundred years if not abused although if exposed to excessive heat or UV they will break down too.
 
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Old 04-15-19, 06:46 PM
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Thanks for the info Ben, It's good to know that BX was manufactured with both rubber insulation as well as plastic. I've seen some in awful condition, and some in decent condition - that's probably why, I didn't think to look closer at the insulation itself.

I wonder what they'll say about those old timers who used NM-B back in the day...
 
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Old 04-15-19, 09:04 PM
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I agree. Left alone in the wall and undisturbed it will function a long time. However..... what you usually see is the ends where it enters a box and more typically in a light fixture box where the insulation is completely gone.
 
 

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